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  <h3>Table of Contents</h3>

  <ul class="link-list" role="directory">
    <li><a href="#label-Miscellaneous+Syntax">Miscellaneous Syntax</a>
    <li><a href="#label-Ending+an+Expression">Ending an Expression</a>
    <li><a href="#label-Indentation">Indentation</a>
    <li><a href="#label-alias"><code>alias</code></a>
    <li><a href="#label-undef"><code>undef</code></a>
    <li><a href="#label-defined-3F"><code>defined?</code></a>
    <li><a href="#label-BEGIN+and+END"><code>BEGIN</code> and <code>END</code></a>
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<main role="main" aria-label="Page syntax/miscellaneous.rdoc">

<h1 id="label-Miscellaneous+Syntax">Miscellaneous Syntax<span><a href="#label-Miscellaneous+Syntax">&para;</a> <a href="#top">&uarr;</a></span></h1>

<h2 id="label-Ending+an+Expression">Ending an Expression<span><a href="#label-Ending+an+Expression">&para;</a> <a href="#top">&uarr;</a></span></h2>

<p>Ruby uses a newline as the end of an expression.  When ending a line with an operator, open parentheses, comma, etc. the expression will continue.</p>

<p>You can end an expression with a <code>;</code> (semicolon).  Semicolons are most frequently used with <code>ruby -e</code>.</p>

<h2 id="label-Indentation">Indentation<span><a href="#label-Indentation">&para;</a> <a href="#top">&uarr;</a></span></h2>

<p>Ruby does not require any indentation.  Typically, ruby programs are indented two spaces.</p>

<p>If you run ruby with warnings enabled and have an indentation mismatch, you will receive a warning.</p>

<h2 id="label-alias"><code>alias</code><span><a href="#label-alias">&para;</a> <a href="#top">&uarr;</a></span></h2>

<p>The <code>alias</code> keyword is most frequently used to alias methods.  When aliasing a method, you can use either its name or a symbol:</p>

<pre class="ruby"><span class="ruby-keyword">alias</span> <span class="ruby-identifier">new_name</span> <span class="ruby-identifier">old_name</span>
<span class="ruby-keyword">alias</span> <span class="ruby-value">:new_name</span> <span class="ruby-value">:old_name</span>
</pre>

<p>For methods, <a href="../Module.html#method-i-alias_method"><code>Module#alias_method</code></a> can often be used instead of <code>alias</code>.</p>

<p>You can also use <code>alias</code> to alias global variables:</p>

<pre class="ruby"><span class="ruby-identifier">$old</span> = <span class="ruby-value">0</span>

<span class="ruby-keyword">alias</span> <span class="ruby-identifier">$new</span> <span class="ruby-identifier">$old</span>

<span class="ruby-identifier">p</span> <span class="ruby-identifier">$new</span> <span class="ruby-comment"># prints 0</span>
</pre>

<p>You may use <code>alias</code> in any scope.</p>

<h2 id="label-undef"><code>undef</code><span><a href="#label-undef">&para;</a> <a href="#top">&uarr;</a></span></h2>

<p>The <code>undef</code> keyword prevents the current class from responding to calls to the named methods.</p>

<pre class="ruby"><span class="ruby-keyword">undef</span> <span class="ruby-identifier">my_method</span>
</pre>

<p>You may use symbols instead of method names:</p>

<pre class="ruby"><span class="ruby-keyword">undef</span> <span class="ruby-value">:my_method</span>
</pre>

<p>You may undef multiple methods:</p>

<pre class="ruby"><span class="ruby-keyword">undef</span> <span class="ruby-identifier">method1</span>, <span class="ruby-identifier">method2</span>
</pre>

<p>You may use <code>undef</code> in any scope.  See also <a href="../Module.html#method-i-undef_method"><code>Module#undef_method</code></a></p>

<h2 id="label-defined-3F"><code>defined?</code><span><a href="#label-defined-3F">&para;</a> <a href="#top">&uarr;</a></span></h2>

<p><code>defined?</code> is a keyword that returns a string describing its argument:</p>

<pre class="ruby"><span class="ruby-identifier">p</span> <span class="ruby-keyword">defined?</span>(<span class="ruby-constant">UNDEFINED_CONSTANT</span>) <span class="ruby-comment"># prints nil</span>
<span class="ruby-identifier">p</span> <span class="ruby-keyword">defined?</span>(<span class="ruby-constant">RUBY_VERSION</span>)       <span class="ruby-comment"># prints &quot;constant&quot;</span>
<span class="ruby-identifier">p</span> <span class="ruby-keyword">defined?</span>(<span class="ruby-value">1</span> <span class="ruby-operator">+</span> <span class="ruby-value">1</span>)              <span class="ruby-comment"># prints &quot;method&quot;</span>
</pre>

<p>You don’t need to use parenthesis with <code>defined?</code>, but they are recommended due to the <a href="precedence_rdoc.html">low precedence</a> of <code>defined?</code>.</p>

<p>For example, if you wish to check if an instance variable exists and that the instance variable is zero:</p>

<pre class="ruby"><span class="ruby-keyword">defined?</span> <span class="ruby-ivar">@instance_variable</span> <span class="ruby-operator">&amp;&amp;</span> <span class="ruby-ivar">@instance_variable</span>.<span class="ruby-identifier">zero?</span>
</pre>

<p>This returns <code>&quot;expression&quot;</code>, which is not what you want if the instance variable is not defined.</p>

<pre class="ruby"><span class="ruby-ivar">@instance_variable</span> = <span class="ruby-value">1</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-ivar">@instance_variable</span>) <span class="ruby-operator">&amp;&amp;</span> <span class="ruby-ivar">@instance_variable</span>.<span class="ruby-identifier">zero?</span>
</pre>

<p>Adding parentheses when checking if the instance variable is defined is a better check.  This correctly returns <code>nil</code> when the instance variable is not defined and <code>false</code> when the instance variable is not zero.</p>

<p>Using the specific reflection methods such as instance_variable_defined? for instance variables or const_defined? for constants is less error prone than using <code>defined?</code>.</p>

<p><code>defined?</code> handles some regexp global variables specially based on whether there is an active regexp match and how many capture groups there are:</p>

<pre class="ruby"><span class="ruby-regexp">/b/</span> <span class="ruby-operator">=~</span> <span class="ruby-string">&#39;a&#39;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-identifier">$~</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$&amp;</span>) <span class="ruby-comment"># =&gt; nil</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$`</span>) <span class="ruby-comment"># =&gt; nil</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$&#39;</span>) <span class="ruby-comment"># =&gt; nil</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$+</span>) <span class="ruby-comment"># =&gt; nil</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$1</span>) <span class="ruby-comment"># =&gt; nil</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$2</span>) <span class="ruby-comment"># =&gt; nil</span>

<span class="ruby-regexp">/./</span> <span class="ruby-operator">=~</span> <span class="ruby-string">&#39;a&#39;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-identifier">$~</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$&amp;</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$`</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$&#39;</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$+</span>) <span class="ruby-comment"># =&gt; nil</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$1</span>) <span class="ruby-comment"># =&gt; nil</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$2</span>) <span class="ruby-comment"># =&gt; nil</span>

<span class="ruby-regexp">/(.)/</span> <span class="ruby-operator">=~</span> <span class="ruby-string">&#39;a&#39;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-identifier">$~</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$&amp;</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$`</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$&#39;</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$+</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$1</span>) <span class="ruby-comment"># =&gt; &quot;global-variable&quot;</span>
<span class="ruby-keyword">defined?</span>(<span class="ruby-node">$2</span>) <span class="ruby-comment"># =&gt; nil</span>
</pre>

<h2 id="label-BEGIN+and+END"><code>BEGIN</code> and <code>END</code><span><a href="#label-BEGIN+and+END">&para;</a> <a href="#top">&uarr;</a></span></h2>

<p><code>BEGIN</code> defines a block that is run before any other code in the current file. It is typically used in one-liners with <code>ruby -e</code>.  Similarly <code>END</code> defines a block that is run after any other code.</p>

<p><code>BEGIN</code> must appear at top-level and <code>END</code> will issue a warning when you use it inside a method.</p>

<p>Here is an example:</p>

<pre class="ruby"><span class="ruby-keyword">BEGIN</span> {
  <span class="ruby-identifier">count</span> = <span class="ruby-value">0</span>
}
</pre>

<p>You must use <code>{</code> and <code>}</code> you may not use <code>do</code> and <code>end</code>.</p>

<p>Here is an example one-liner that adds numbers from standard input or any files in the argument list:</p>

<pre>ruby -ne &#39;BEGIN { count = 0 }; END { puts count }; count += gets.to_i&#39;</pre>

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